Electric heater



June 25, 1957 P. L. FOWLER ETAL ELECTRIC, HEATER 2 Sheets-Shae:

Filed July 25. 1955 INVENTORS PAUL L. FOWLER CHESTER A. ARTHUR BY I M4444/ s, ATTORNEYS June 25,195? P. L. FOWLER ETA}, 2,

ELECTRIC HEATER V V Filed-M1125, 1955 2 Sheets-Sheet 2 INVENTORS PAUL L.FOWLER h CHESTER A. ARTHUR AT oR NEYS United States Patent O ELECTRICHEATER Paul L. Fowler, Portland, and Chester A. Arthur, Jennings Lodge,Oreg.

Application July 25, 1955, Serial No. 524,020

Claims. (Cl. 219-38) This invention relates to improvements in electricheaters, and has particular reference to improvements in bandtypeheaters for water tanks and the like.

An object of the invention is to provide an improved electric heatingelement of general application which may be economically manufacturedfor different voltage and current ratings.

Another important object of the invention is to provide a band-typeelectric heater for water tanks which has an improved arrangement ofheating units for applying thermal energy to the outside of a tank orother surface to be heated.

A further object is to provide a band-type electric heater having aplurality of heating units which are conveniently and quickly assembledinto a unitary heater structure conformable to a curved surface.

A further object is to provide a band-type electric heater which isreadily applicable as a replacement or addition to most types ofexisting hot water tanks.

A further object is to provide a heater having a plurality of heatingunits which may be assembled in variable number according to the heatingeffect desired and wherein the failure of one unit will not seriouslyimpair the operation of the heater.

A further object is to provide a heater having a plurality of unitswhich are readily individually replaceable when defective.

A still further object is to provide an improved heating element whichcomprises a flexible web utilizing glass fiber threads and a resistorwire.

An additional object is to provide an improved heating element structurewhich is initially formed into a narrow continuous web composed ofdielectric threads and a resistor wire and which may be severed in shortlengths to form individual heating elements.

Still another object is to provide a heating element of the typedescribed which may be fabricated on a conventional weaving or knittingmachine, or the like, in strip form and then cut to lengths appropriatefor the voltage to be applied and the temperature to be developed.

The improvements set forth in the above objects are accomplished by aheater structure utilizing certain novel component parts assembled innovel arrangement. The heater is of the band type which is arranged toencircle a metallic water tank and heat the water therein by conductionof thermal energy through the tank. The heater employs a plurality ofnovel heating units adapted to be held in contact with the outer tanksurface in eflicient heat transfer relation. The improvements obtainedare accomplished by the heating unit structure providing as one featurethe use of a novel heating element comprising a web of glass fiberthreads and resistor wire which is initially formed in a continuous,narrow strip and subsequently severed into lengths desired.

The invention will be better understood and additional objects andadvantages will become apparent from the following description taken inconnection with 2,797,296. Patented June 25, 1957 the accompanyingdrawings which illustrate a preferred form of the invention. It is to beunderstood, however, that the invention may take other forms, and thatall such modifications and variations within the scope of the appendedclaims which will occur to persons skilled in the art are included inthe invention.

In the drawings:

Figure l is a perspective view of the heater of the present, inventionshown in band form and having a plurality of individual heating unitsthereon;

Figure 2 is a plan view of the heater laid out in flat condition andprior to mounting on a water tank;

Figure 3 is a sectional view taken on the line 3--3 of Figure 2;

Figure 4 is a fragmentary side elevational view taken on the line 4-4 ofFigure 2;

Figure 5 is a perspective view of a water tank with parts broken awayshowing the present heater applied thereto;

Figure 6 is an enlarged exploded view of one of the individual heatingunits;

Figure 7 is an enlarged fragmentary plan view of one form of heatingelement comprising a woven web;

Figure 8 is a sectional view taken on the line 8-8 of Figure 7; and

Figure 9 is an enlarged fragmentaryplan View of another form of heatingelement comprising a knitted web.

Referring specifically to the drawings, the numeral 10 designates,generally, the heater of the present invention. This heater is aband-type heater and, although it may be used for applying thermalenergy to various surface areas, it is described herein as being appliedto a metallic water tank 12, Figure 5, which is in ordinary domesticuse. In conventional constructions, an outer casing 13 is providedaround the tank 12, and disposed between the tank and casing is aninsulation blanket 14 and a dead air space 15.

The heater 10 utilizes a plurality of heating units, designatedgenerally by the numeral 20 and shown in detail in Figure 6. Each of theheating units 20 comprises a heating element 22 which, in assembledrelation, is disposed between sheets of insulation material 23 and 24.The sheet 23 is preferably mica, and the sheet 24 is preferably formedof an asbestos material. The casing for the heating unit 20 comprises abody member 27 having side flanges 28 and a cover portion 39 providedwith a pair of tabs 31 struck out of the metal. The casing parts 27 and30 are formed from a soft metal, preferably aluminum, and the parts ofthe unit are held in tightly layered position by bending the flanges 28over into firm engagement with the cover 30, as shown in Figure 4.

The unit parts 22, 24 and 30 are provided with apertures 33, 34 and 35,respectively, adjacent the ends thereof for receiving a smooth,upstanding shank 36 of a headed pin 37 which, as will be described,forms a terminal post for the heating unit, the pin 37 preferably beingformed of a soft metal such as aluminum. Apertures 35 in the coverportion 30 are enlarged relative to the diameter of the pin shank 36 sothat clearance is provided around said pins to prevent electricalcontact between the pins and the cover 30. A pair of washers 38, formedof a dielectric material, are disposed on opposite faces of the cover 30at each end thereof. The cover is embossed at 39 forming an annularinset to center one of the washers 38 on each terminal post aperture 35.

The heating element 22 comprises a web of material, best shown inFigures 7 and 8, having interwoven glass threads 40 and a resistor wire41. The heating element 22 is woven in a well known manner with theglass threads 40 forming the warp of the material and the resistor wire41 forming the filler of woof of the material. The resistor wire 41 isinterlaced back and forth with connecting "loops 42 on the ends betweenadjoining'strands, and the web material is preferably formed in longstrips by conventional weaving machines and then merely cut to thedesired length for use in the heating unit. Each of the interlacedstrands of the resistor wire is held in spaced relation from theadjoining strands by the warp material 40.

Referring to Figures 1-4, the supporting structure of the heatercomprises an end bracket 45 and an intergral flexible band member 46, towhich the individual heating units are attached by means of the tabs 31which are bent over to engage said band. A pair of strap members 48 aresecured to the band 46, and the ends of these straps are engageable in apair of clamps 49 on the bracket 45, whereby the heater can be loopedaround a water tank and held snugly thereon by engagement of the straps48 in the clamp members 49.

Disposed adjacent the sides of the band 46 is a pair of bus bars 52 and53 having apertures suitably spaced for receiving the projecting shankportions 36 of the pins 37 and for electrically connecting a pluralityof the heating units 2%? in parallel. The bus bars 52 and 53 are held inpositive engagement with the shanks 36 by means of hardened spring nuts54 having opposed spring tongues 55 provided with teeth edges forgripping positively into the soft metallic shank without requiringthreads on the shank. These spring nuts are movable in only onedirection on the shanks 36 by reason of pawl action of the teeth edges,and, therefore, when pressed down tightly on the shanks, the parts 22,24 and of the heating units are compressed firmly together and a goodelectrical connection is established between the heads of the pins 37and underlying strands of the resistor wire 41. Apertures 33 in theheating element are not made in a manner to sever the resistor wire 41but preferably by merely forcing the shanks 36 between the strands ofglass and wire whereby the head of the pin will bear against severalreaches of the wire at the point of electrical connection.

The bus bars 52 and 53 are secured to the bracket by screws 56 whichform terminals, and said bus bars and screws are insulated from thebracket by suitable dielectric washers 57. The heater is energized by apair of lead wires 64 and 61. Lead wire 60 is electrically connected toone of the terminals 56, and the lead Wire 61 is connected to anadjustable automatic thermostat 62 mounted on the bracket 45. Thermostat62 is electrically connected in series between the lead wire 61 and thebus bar 53 by means of a wire 63 connected to the other terminal 56.

An important feature of the present heater structure is that it iseasily and quickly assembled by workmen. The units 20 are readilyassembled by laying the heating element 22, insulation sheets 23 and 24,and cover 30 in the body portion 27 and then bending flanges 28 intoclamping engagement with the cover. The flanges 28 hold the parts incompact relationship, and, as described herein before, a good electricalconnection between the pin 37 and the element 22 is accomplished by thespring nuts 54 which are adapted eflectively to compress the three toplayers together as well as to draw the heads of the pins 37 into firmengagement with the resistor wire of the heating element. The individualheating units 20 are readily mounted on the band 46 by means of the tabs31 and are more positively held in fixed position against sliding on theband 46 by the bus bars 52 and 53.

As the web for the element 22 is woven in a long strip and the resistorwire is disposed in transverse strands, lengths may be cut from saidstrip to provide elements having any desired wattage at a given voltage.The glass thread being refractory, the heating element may be operatedat a red heat if desired. The element is thus suitable for toasters andother radiant heaters without being enclosed, as shown in Figure 6. Whenoperated at lower temperatures the flexibility of the element 22 makesit suitable for heating pads, garments and other shape-conformingapplications.

Another advantage of the present form of construction is that the numberof individual units 20 may be varied on the heater structure to increaseor decrease the thermal capacity thereof, as desired. When the heater iscinched up tightly on a round tank, the individual units 2%} aresutficiently yieldable to become curved to conform to the shape of thetank and provide good heat transfer by conduction. The insulation sheet23 electrically insulates the element 22 from the body portion 27 butpermits thermal energy to be transmitted readily from the element to thebody portion. The other insulation sheet provides thermal as well aselectrical insulation on the back of the unit.

The present invention, therefore, provides an improved heater forapplication to surface areas which has inexpensive component partsreadily and quickly assembled by workmen. The invention resides in thecomponent parts of the heater structure as well as the combinationitself. Therefore, it is evident that the individual heating units 20could be used in other types of structure than that shown and theheating element 22, similarly, may be used for other purposes notconnected with the unit parts 20.

Figure 9 shows another form of heating element comprising a web ofmaterial 22 formed by conventional knitting processes. As seen, theknitted web is formed from two strands 65 and 66, the strand 65 shown infull lines comprising the resistor wire and the strand 66 shown indotted lines, comprising a dielectric refractory strand such as glassthread. Most forms of knitting may be used to make the web 22, as longas the glass thread 66 separates transverse courses of the resistorwire. The particular type of web shown in Figure 9 is made by the jerseystitch, and may be made on conventional knitting machines.

In the jersey stitch, the transverse courses of resistor wire 65comprise a plurality of loops 68, and the various courses of saidresistor wire are held in spaced relation by the glass thread 66,comprising interconnecting loops 69. The web 22 is initially formed withan end interiocking portion 70 of glass thread, and is knitted in stripform having a predetermined width for assembly in desired sizes ofheating units. The resistor wire 65 is a single continuous wire and theadjoining courses are connected by size portions 71 interlaced with sideportions 72 of the glass thread 66 in the usual manner of knitting arectangular web or tape.

The heating element strip 22 may be severed transversely into desiredlengths for providing heating units 20 of desired wattage at a givenvoltage. When installed in a heating unit 20, the headed pins 36 areforced through the web and each pin engages at least one of thetransverse courses of resistor wire to form an electrical connectiontherewith. The heating element is clamped firmly between the insulatingsheets of the heating unit and can in no way unravel from its knittedform.

Having now described our invention and in what manner the same may beused, what we claim as new and de' sire to protect by Letters Patent is:

l. A band-type electric heater comprising an elongated flat band offlexible material, a transverse bracket on one end of said bandprojecting beyond the width of the band, bus bars mechanically connectedwith the ends of said bracket and extending parallel with said band inspaced relation beyond the opposite side edges thereof, heating units inindividual flexible metal casings disposed side by side along said bandwith end portions projecting over the side edges of said band andconnected with said bus bars, bendable tabs on said heating unitsengaging the edges of said band, straps on the other end of said band,and clamps for said straps on said bracket.

2. A band-type heater structure for a water tank and the like,comprising a plurality of flat heating units disposed in parallelrelation, support means for holding said heating units in surfaceengagement with said tank, a heating element in each of said heat-ingunits comprising an interwoven web of resistor wire and dielectricthreads, 21 pair of spaced terminal posts on each of said heating units,said terminal posts being electrically connected to said heating elementand having an outwardly projecting portion, a pair of electricalconductors engageable with the projecting portions of said terminalposts for supplying electric energy to said heating elements, andfastening means engageable on said terminal posts arranged firmly tohold said electric conductors thereon and to urge said terminal postsinto positive engagement with said heating element.

3. An electric heater comprising an elongated supporting band, bus barsextending along said band in spaced relation beyond opposite side edgesthereof, a plurality of heating units having end portions projectingbeyond said opposite side edges of said band, bendable tabs on saidheating units engaging said band, heating elements in said units, headedterminal pins piercing said elements and projecting from. said endportions of said units, and spring nuts on said pins securing said pinsto said bus bars and clamping. the heads of said pins against saidheating elements.

4. In an electric heater, a heating element, headed terminal pins havingsmooth, soft metal shanks piercing said element, bus bars for energizingsaid heating elements, and hard metal spring nuts having biting jawsengaging said shanks to secure said pins to said bus bars and clamp theheads of the pins against said heating elements.

5. In a heater structure, a heating unit comprising a heating element,said heating element being composed of a fiat interwoven web of glassthreads and a resistor wire, a casing for said heating element, andelectrical connecting means comprising headed metal pins forced throughthe mesh of said Web frictional'ly engaging said element and extendingoutwardly through said casing.

6. A heating unit comprising a casing, said casing being composed of abody portion having cover means and foldab'le tabs arranged to fold intoengagement with said cover means for quick assembly and disassembly ofsaid casing, a heating element insulatedly mounted in said body portion,said heating element comprising a fiat fabricated web of glass threadand a resistor wire, and electrical connecting means comprising headedterminal pins forced through the mesh of said web frictionally engagingsaid resistor wire.

7. A heating element comprising a web of straight, parallel glass fiberthreads and a bare, uniform resistor wire interlaced in a plain weave.

8. A heating element in the form of an interwoven web comprising as thewarp straight, parallel dielectric refractery threads and comprising asthe filler a bare, uniform resistor wire.

9. A flexible heating element comprising a bare resistor Wire and aglass fiber thread knitted together in interlacing loops in the form ofa fabric wherein the wire loops and thread loops are of the same sizeand configuration.

10. A flexible heating element comprising a web having a Warp of glassfiber threads disposed in parallel side-bysi-de relation without anyappreciable openings therebetween, and a resistance wire fillerinterlaced with said Warp threads in a plain substantially tight weave.

References Cited in the file of this patent UNITED STATES PATENTS1,321,462 Line Nov. 11, 1919 1,642,197 Fowler Sept. 13, 1927 1,704,413Wait Mar. 5, 1929 1,992,593 Whitney Feb. 26, 1935 2,022,662 Geyser Dec.3, 1935 2,157,606 Harris May 9, 1939 2,284,653 Hackethal June 2, 19422,375,997 Larson May 15, 1945 2,572,695 Briscoe et al Oct. 23, 1951

